Remove 'config.py' from the distribution

The source file 'config.py' is auto generated from config.py.in, so it
should not be contained in the distribution (generated by 'make dist').
This patch moves it to nodist file list according to
http://www.gnu.org/software/automake/manual/html_node/Python.html

Another change in patch is removing the unnecessary temp var 'SOURCE'.

Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>